Organic electroluminescent device and method of manufacturing the same

ABSTRACT

The invention provides an organic electroluminescent device and a method of manufacturing the same which conveniently reduce or suppress the transfer of ionic impurities into a light-emitting layer, and reduce or prevent the light-emitting property in the light-emitting layer from degrading, which promotes life extension. An organic electroluminescent device includes a functional layer having at least a light-emitting layer between a first electrode and a second electrode. At least a part of the functional layer is formed of the inorganic ion exchange material added to the functional material to form the functional layer.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an organic electroluminescent deviceand a method of manufacturing the same with an enhanced light-emittingproperty by selective trapping and fixation of mobile ions.

2. Description of Related Art

Related art organic electroluminescent elements (hereinafter “organic ELelements”) using an organic substance in a light-emitting layer can beused as a spontaneous emission display. A significant issue with organicelectroluminescent devices that have such organic electroluminescentelements is the life extension of the elements. Thus, a technology topromote the life extension of the elements is advantageous.

Accordingly, related art electroluminescent elements (organicelectroluminescent devices), in which a device to apply a voltage in adirection opposite to the emitting electric field is provided in adevice to apply a voltage between an anode and a cathode, is disclosedin Japanese Unexamined Patent Application Publication No. 9-293588, forexample. The provision of such devices allows, for example, theorientation polarization of a functional group, which is a part of theorganic compound composing the light-emitting layer when emitting, orthe ionic polarization of ionic impurities, to be reduced or suppressedin advance by applying a voltage to the opposite direction beforeemitting light for the first time, and allows ionic impurities (mobileions) to be prevented from being transferred and diffused into thelight-emitting layer. As a result, the light-emitting property could beprevented from degrading or such degradation could be reduced in thelight-emitting layer caused by the ionic impurities, and the lifeextension of the electroluminescent elements (organic electroluminescentdevices) could be promoted.

SUMMARY OF THE INVENTION

However, the electroluminescent element (organic electroluminescentdevice) prevents the transfer of ionic impurities by its drive method,and prevents the light-emitting property from degrading in thelight-emitting layer. Naturally, the drive system in such anelectroluminescent element (organic electroluminescent device) becomescomplicated, and eventually brings about a new issue, which maycomplicate the construction of the device.

The present invention addresses the above and/or other situations, andprovides an organic electroluminescent device and a method ofmanufacturing the same which can conveniently reduce or prevent theionic impurities from transferring into the light-emitting layer, andeventually reduce or prevent the light-emitting property from degradingin the light-emitting layer and promote life extension.

To address or achieve the above, the present invention provides anorganic electroluminescent device including a functional layer having atleast a light-emitting layer between a first electrode and a secondelectrode. At least a part of the functional layer is formed by using afunctional material with an inorganic ion exchange material.

According to the organic electroluminescent device, at least a part ofthe functional layer is formed of an inorganic ion exchange materialadded to the functional material to form the functional layer. Thus, ifionic impurities are included in the functional layer with the additionof the inorganic ion exchange material, the ionic impurities can beprevented from diffusing, or such diffusion can be reduced, into thelight-emitting layer by trapping and fixation onto the inorganic ionexchange material, and the degrading of the light-emitting property canbe reduced or prevented. Also, when the ionic impurities included ineach of the electrodes or other functional layers become mobile ions anddiffuse, the trapping and fixation onto the inorganic ion exchangematerial will reduce or prevent the ionic impurities from diffusing into the light-emitting layer.

Further, in the organic electroluminescent device, preferably, thefunctional layer has a carrier injection/transport layer, and thefunctional layer formed by adding the inorganic ion exchange material isa hole injection/transport layer functioning as the carrierinjection/transport layer.

When done this way, the mobile ions (ionic impurities) existing in thematerial to form the hole injection/transport layer will be trapped andfixated onto the inorganic ion exchange material. Thus, thelight-emitting property is prevented from degrading, or such degradationis reduced, in the light-emitting layer caused by the mobile ions.

Also, in this case, it is preferable that the inorganic ion exchangematerial be antimony pentoxide hydrate.

Antimony pentoxide hydrates have high selective absorption to Na ions.If the Na ions exist in the material to form the holeinjection/transport layer, these Na ions can be satisfactorily trappedand fixated to prevent them from diffusing.

Further, in the organic electroluminescent device, the functional layerformed by adding the inorganic ion exchange material may be thelight-emitting layer.

When done this way, even if the mobile ions (ionic impurities) diffuseinto the light-emitting layer, they will be trapped and fixated by theinorganic ion exchange material. Thus, the light-emitting property isprevented from degrading, or such degradation is reduced, in thelight-emitting layer caused by these mobile ions.

Further, in the organic electroluminescent device, the functional layermay have a carrier injection/transport layer, and the functional layerformed by adding the inorganic ion exchange material may be an electroninjection/transport layer functioning as the carrier injection/transportlayer.

When done this way, the mobile ions (ionic impurities) existing in thematerial to form the electron injection/transport layer will be trappedand fixated onto the inorganic ion exchange material. Thus, thelight-emitting property is prevented from degrading, or such degradationis reduced, in the light-emitting layer caused by these mobile ions.

The present invention provides another organic electroluminescent deviceincluding a functional layer having at least a light-emitting layerbetween a first electrode and a second electrode, in which an inorganicion exchange layer, formed of an inorganic ion exchange material, isprovided between the first electrode and the second electrode.

According to the organic electroluminescent device, an inorganic ionexchange layer is provided between the first electrode and the secondelectrode. Thus, if ionic impurities included in each of the electrodesor functional layers, such as the hole injection/transport layer, becomemobile ions and diffuse, they will be trapped and fixated by theinorganic ion exchange layer, preventing the light-emitting propertyfrom degrading, or reducing such degradation, caused by the ionicimpurities diffusing into the light-emitting layer.

Further, in the organic electroluminescent device, it is preferable thatthe functional layer has a hole injection/transport layer between thefirst electrode and the light-emitting layer, and the inorganic ionexchange layer be provided between the hole injection/transport layerand the light-emitting layer.

When done this way, the mobile ions (ionic impurities) existing in thematerial to form the hole injection/transport layer will be trapped andfixated at the inorganic ion exchange layer. Thus, the light-emittingproperty is prevented from degrading, or such degradation is reduced, inthe light-emitting layer caused by these mobile ions diffusing into thelight-emitting layer.

Further, in the organic electroluminescent device, it is preferable thatthe functional layer has an electron injection/transport layer betweenthe second electrode and the light-emitting layer, and the inorganic ionexchange layer be provided between the electron injection/transportlayer and the light-emitting layer.

When done this way, the mobile ions (ionic impurities) existing in thematerial to form the electron injection/transport layer will be trappedand fixated at the inorganic ion exchange layer. Thus, thelight-emitting property is prevented from degrading, or such degradationis reduced, in the light-emitting layer caused by these mobile ionsdiffusing into the light-emitting layer.

The present invention also provides a method of manufacturing an organicelectroluminescent device that includes a functional layer having alight-emitting layer and a carrier injection/transport layer between afirst electrode and a second electrode. The method includes: adding aninorganic ion exchange material to a functional material, and forming atleast a part of the functional layer using the obtained functionalmaterial.

According to the method of manufacturing an organic electroluminescentdevice, at least a part of the functional layer is formed with theinorganic ion exchange material added to the functional material to formthe functional layer. If ionic impurities are included in the functionallayer with the addition of inorganic ion exchange material, they will betrapped and fixated onto the inorganic ion exchange material, therebypreventing the light-emitting property from degrading, or reducing suchdegradation, caused by the ionic impurities diffusing into thelight-emitting layer. Also, when ionic impurities included in each ofthe electrodes or other functional layers become mobile ions anddiffuse, they will be trapped and fixated onto the inorganic ionexchange material, preventing the light-emitting property fromdegrading, or reducing such degradation, caused by the ionic impuritiesdiffusing into the light-emitting layer.

Further, in the method of manufacturing an organic electroluminescentdevice, it is preferable that the functional material with the additionof the inorganic ion exchange material be disposed by ejecting liquiddroplets, to form the functional layer.

When done this way, it will be possible to precisely distribute thefunctional material with the addition of the inorganic ion exchangematerial at the desired location, and thus, for example, selectivelydistribute the inorganic ion exchange material corresponding to thelight-emitting layer's color.

The present invention also provides another method of manufacturing anorganic electroluminescent device that includes a functional layerhaving at least a light-emitting layer between a first electrode and asecond electrode in which an inorganic ion exchange material is disposedbetween the first electrode and the second electrode to form aninorganic ion exchange layer.

According to the method of the manufacturing the inorganicelectroluminescent device, an inorganic ion exchange layer is formedbetween the first electrode and the second electrode. Thus, when theionic impurities included in each of the electrodes or the holeinjection/transport layer become mobile ions and diffuse, they will betrapped and fixated at the inorganic ion exchange layer, preventing thelight-emitting property from degrading, or reducing such degradation,caused by the ionic impurities diffusing into the light-emitting layer.

Furthermore, in the method of manufacturing the organicelectroluminescent device, it is preferable that the inorganic ionexchange material be disposed by ejecting liquid droplets, to form theinorganic ion exchange layer.

When done this way, it will be possible to precisely distribute theinorganic ion exchange material at the desired location, and thus, forexample, selectively distribute the inorganic ion exchange materialcorresponding to the light-emitting layer's color.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of significant parts of an organicelectroluminescent device according to the present invention;

FIG. 2 is a schematic explaining a method of manufacturing the organicelectroluminescent device;

FIGS. 3A–3C are schematics of the processes subsequent to the processshown in FIG. 2;

FIG. 4 is a sectional side view of significant parts of another organicelectroluminescent device according to the present invention; and

FIG. 5 is a sectional side view of significant parts of still anotherorganic electroluminescent device according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detailbelow.

First Exemplary Embodiment

FIG. 1 is a sectional side view showing significant parts of an organicelectroluminescent device according to a first exemplary embodiment ofthe present invention. FIG. 1 shows the organic electroluminescentdevice 1. The organic electroluminescent device 1 has a transparentelectrode 3 (a first electrode) and a cathode 4 (a second electrode) ona substrate 2 thereof, and has a functional layer 5 between thetransparent electrode 3 and the cathode 4, with the light emitted in thefunctional layer 5 being emitted from the substrate 2 side, which isreferred to as a bottom emission type.

In the substrate 2, driving elements (not shown) composed of TFTelements, or various wiring lines, are formed on a transparentsubstrate, such as a glass substrate (not shown), and transparentelectrodes 3 are formed on the corresponding driving elements or variouswiring line via an insulating film or a flattening film.

The transparent electrodes 3 are patterned in corresponding single dotareas to be formed on the substrate 2, and are respectively connected tothe driving elements composed of TFT elements, or various wiring lines.In the present invention, the transparent electrodes are formed ofindium tin oxide (ITO).

An inorganic bank 6 and an organic bank 7 are formed around thetransparent electrode 3 to define a single dot area, and the functionallayer 5 is provided in a concave portion surrounded by the inorganicbank 6 and the organic bank 7.

Particularly, in the dot area that emits red or green light, thefunctional layer 5 includes a hole injection/transport layer 8 and alight-emitting layer 9, as shown in FIG. 1. Further, in the dot areathat emits green light, an electron injection/transport layer (notshown) is provided on the light-emitting layer 9 in addition to the holeinjection/transport layer 8 and the light-emitting layer 9.

The hole injection/transport layer 8 is formed of a material obtained byadding an inorganic ion exchange material to an original material toform the hole injection/transport layer.

In other words, as the original material to form the holeinjection/transport layer, a dispersion solution of3,4-polyethylenedioxythiophene/polystylene sulfonic acid (PEDOT/PSS)[Brand name: “Bytron-p” made by Bayer AG], i.e., a dispersion solutionwhich is obtained by dispersing 3,4-polyethylenedioxythiophene inpolystyrene sulfonic acid as the dispersion medium, and dispersing theresultant again in water may be adequately used. Here, Na ions as ionicimpurities with a concentration close to hundreds of ppm is contained inthis formation material, and the Na ions may diffuse as mobile ions.

Accordingly, in the present exemplary embodiment, a dispersion solution,which is obtained by adding an inorganic ion exchange material to suchmaterial, is used.

The inorganic ion exchange material is composed of metal salt, such asmetallic oxide, and includes the type that adsorbs positive ions to trapand fixate these ions, the type that adsorbs negative ions to trap andfixate these ions, and the type that adsorbs both the positive andnegative ions to trap and fixate these ions.

The inorganic ion exchange material to trap and fixate positive ions mayinclude antimony pentoxide (Sb₂O₅) hydrates (for example, IXE[registered trademark]-300 made by Toagosei. Co., Ltd.)), titaniumphosphate (for example, IXE [registered trademark]-400 made by Toagosei.Co., Ltd.), or zirconium phosphate (for example, IXE [registeredtrademark]-100 made by Toagosei. Co., Ltd.). Antimony pentoxide hydratesespecially have a high selective absorption to Na ions and are thussuitable as an inorganic ion exchange material added to the originalmaterial to form the hole injection/transport layer. The reason for thisis that many Na ions are included as the ionic impurities in theoriginal material to form the hole injection/transport layer aspreviously described, and they become mobile ions which may degrade thelight-emitting property in the light-emitting layer 9.

Further, the inorganic ion exchange material to trap and fixate negativeions may include the hydrous bismuth oxide (for example, IXE [registeredtrademark]-500 made by Toagosei. Co., Ltd.), or lead phosphate hydroxide(for example, IXE [registered trademark]-1000 made by Toagosei. Co.,Ltd.). Since hydrous bismuth oxide especially have a high selectiveabsorption to sulphate (SO₄ ⁻²) ions, it is suitably used as aninorganic ion exchange material added to the original material to formthe hole injection/transport layer together with the aforementionedantimony pentoxide hydrates. In other words, the original material toform the hole injection/transport layer uses polystyrene sulfonic acidas the dispersion medium. Thus, when Na ions are trapped and fixated inthe antimony pentoxide hydrates, free sulphate ions increase and thefree sulphate ions become mobile ions and diffuse, which may degrade thelight-emitting property of the light-emitting layer 9. Therefore, byadding the aforementioned hydrous bismuth oxide, the free sulphate ionsare trapped and fixated, making it possible to prevent the degrading ofthe light-emitting property of the light-emitting layer 9 or reducingsuch degradation.

The inorganic ion exchange material to adsorb both positive and negativeions to trap and fixate these ions may include zirconium oxide orhydrous zirconium oxide, hydrous titanium oxide, and furthermore,substances in the antimony or bismuth system (for example, IXE[registered trademark]-600 or IXE [registered trademark]-633), which ismade by Toagosei. Co., Ltd.). When using such type, a simultaneoustrapping and fixation of both the Na ions included in the originalmaterial to form the hole injection/transport layer and the freesulphate ions can be expected.

Also, in the present exemplary embodiment, antimony pentoxide hydratesare used as an inorganic ion exchange material, and is added to theoriginal material to from the hole injection/transport layer, therebyforming a hole injection/transport layer 8.

As the material to form the light-emitting layer 9, a related art orknown material capable of emitting fluorescent light or phosphorescenceis used. In the present exemplary embodiment, particularly, the luminouswavelength bands corresponding to the three primary colors of light areused to achieve full color display. That is, three light-emitting layers(dots) including a light-emitting layer corresponding to red, alight-emitting layer corresponding to green, and a light-emitting layercorresponding to blue, constitute a pixel. The light-emitting layersemit light with grayscales, so that the organic electroluminescentdevice 1 can perform a full color display.

As the specific material to form the light-emitting layer 9, polymericmaterials, such as the polysilane system including (poly)-fluorene (PF)derivatives, (poly)-paraphenylenevinylene (PPV) derivatives,polyphenylene (PP) derivatives, polyparaphenylene (PPP) derivatives,polyvinylcarbazole (PVK) derivatives, polythiophene derivatives andpolymethyl phenylsilane (PMPS) derivatives are suitably used.

Further, materials obtained by doping the above-mentioned polymericmaterials with polymeric materials, such as perylene based pigments,coumarin pigments and rhodamine pigments, or low molecular materials,such as rubrene, perylene, 9,10-diphenylanthracene,tetraphenylbutadiene, Nile red, coumarin 6, quinacridon can also beused.

The cathode 4 is formed to cover the entire pixel area, and is formed bysequentially laminating a Ca layer and an Al layer from thelight-emitting layer 9 side.

Further, a sealing layer 11 is formed on the cathode 4. The sealinglayer 11 can have a known construction that is formed by a protectivelayer, an adhesive layer and a sealed substrate.

In order to manufacture the organic electroluminescent device 1 havingsuch a construction, TFTs or various wiring lines is first formed on atransparent substrate in the same way as in a related art or theconventional manner, and an interlayer insulating film or a flatteningfilm is then formed, thereby obtaining the substrate 2.

Next, an ITO film is formed on the substrate 2 by a vapor depositionmethod, and a transparent electrode 3 is formed by patterning.

Subsequently, an inorganic bank 6 formed of SiO2 is formed on thesubstrate 2 so as to surround the transparent electrode 3, and anorganic bank 7 formed of resin is also formed on the inorganic bank 6,so that a concave portion 12 is formed in the transparent electrode 3,as shown in FIG. 2. Materials used for the organic bank 7 may includepolyimide or acrylic resin. Materials in which elemental fluorine isincluded in those materials in advance may also be used.

Next, as shown in FIG. 2, the wettability on the substrate in which theconcave portion 12 is surrounded by the inorganic bank 6 and the organicbank 7 is controlled by the consecutive plasma treatment of oxygenplasma-CF4, and a hole injection/transport layer 8 is formed inside theconcave portion 12 by a liquid droplet ejection method, such as an inkjet method. Here, an inorganic ion exchange material (antimony pentoxidehydrates) added to the original material to form the holeinjection/transport layer as previously described, is used to form thehole injection/transport layer 8. However, this inorganic ion exchangematerial is powdered. If the grain size is not small enough, a liquiddroplet ejection head (an ink jet head) may get stuck. Thus, it ispreferred that the grain size be adjusted under a predetermined valueand then be used.

Specifically, for example, antimony pentoxide hydrate (IXE [registeredtrademark]-300 made by Toagosei. Co., Ltd.) is added to the originalmaterial (a dispersion solution of PEDOT/PSS) to form the holeinjection/transport layer until it reaches 1 percent by weight, and isagitated for a predetermined period of time (for instance, 18 hours).Then, the obtained liquid is filtered through a filter with a mesh sizeof 1.0 μm. Subsequently, the obtained filtrate is filtered again,through a filter with a mesh size of 0.5 μm, whereby the powders withdiameters over 0.5 μm are removed from the material.

With the material made through this process, this material isselectively ejected as liquid droplets 8 a into the concave portion 12from a liquid droplet ejection head (ink jet head) 13, as shown in FIG.3A, and when this is continued, a hole injection/transport layer 8 isformed on the transparent electrode 3, as shown in FIG. 3B.

Next, as shown in FIG. 3C, a light-emitting layer 9 is formed on thehole injection/transport layer 8 within the concave portion 12. Theliquid droplet ejection method (ink jet method) is also suitably adoptedto form the light-emitting layer 9. In other words, when forming thelight-emitting layer 9, each of the light-emitting layers for red, greenand blue must be made independently, but according to the liquid dropletejection method, the formation material for each of the light-emittinglayers is separately implanted simply at the desired location, whichmakes it possible to easily form each of the light-emitting layers.

Next, a Ca film is formed with the light-emitting layer 9 and theorganic bank 7 being covered therewith by a vapor deposition method inthe same way as in the related art or conventional manner, and an Alfilm is formed on the Ca film, thereby forming a cathode 4 of a Ca/Allayered structure. Particularly, in the case of the blue light-emittinglayer, an electron injection/transport layer may be formed using a maskwith the selective vapor deposition of LiF on the blue light-emittinglayer, but this is not described in detail below.

Thereafter, a protective layer and an adhesive layer are formed on thecathode 4, and further by adhering a sealed substrate, an organicelectroluminescent device 1 shown in FIG. 1 can be attained.

In the organic electroluminescent device 1 obtained as described above,an inorganic ion exchange material is added to the holeinjection/transport layer 8 to form it. Thus, mobile ions, such as Naions or sulphate ions in the material to form the holeinjection/transport layer, will be trapped and fixated by the inorganicion exchange material and will be kept confined inside the holeinjection/transport layer 8, thereby preventing the mobile ions fromdiffusing, or reducing such diffusion, into the light-emitting layer 9and shortening the lifespan, as a result of that the life extension canbe attained.

Further, by trapping and fixating the Na ions by the inorganic ionexchange material and keeping the Na ions confined inside the holeinjection/transport layer 8, the Na ions can be prevented fromdiffusing, or such diffusion can be reduced, into the TFT element sideof the substrate 2, and characteristics of the TFT element can beprevented from being damaged or such damage can be reduced.

Moreover, for example, even when the In ions or Sn ions in thetransparent electrode 3 diffuses, they can be trapped and fixated in thehole injection/transport layer 31 with the inorganic ion exchangematerial and can be prevented from diffusing, or such diffusion can bereduced, into the light-emitting layer 9. As a result, the degrading ofthe light-emitting property, i.e., shortening of the lifespan can bereduced or prevented.

EXPERIMENTAL EXAMPLE

A transparent electrode formed of ITO is formed on a substrate 2, and onthe transparent electrode, a material (a material obtained fromfiltering twice and adjusting the diameter of the inorganic ion exchangematerial) used to form a hole injection/transport layer 8 is used toform a film by a spin coating method, thereby forming a holeinjection/transport layer.

Next, a light-emitting material that emits green color light is appliedon the hole injection/transport layer by a liquid droplet ejectionmethod, thereby forming a light-emitting layer.

Thereafter, a Ca film and an Al film are respectively formed on thelight-emitting layer in this order by a vapor deposition method to forma cathode composed of a Ca/Al layered structure, and after sealing, theexperimental example of the organic electroluminescent device accordingto the present invention is attained.

For comparison, a hole injection/transport layer formed of the originalmaterial without the addition of an inorganic ion exchange material wasformed, and the rest is manufactured in the same way as in the exemplaryembodiment, so that the organic electroluminescent device as acomparative example was attained.

After measuring the lifespan of each of these organic electroluminescentdevices formed as previously described, the exemplary embodiment had alifespan 1.6 times longer than the comparative example, and it could beconfirmed that, by adding the inorganic ion exchange material, the lifeextension of light-emitting elements can be accomplished.

Further, the lifespan measured here was the period of time for theluminance to drop to half of its initial value. Also, the results of theincrease in a drive voltage measured until the luminance dropped down toits half showed that the exemplary embodiment was suppressed by 0.68times from the experimental example.

Second Exemplary Embodiment

FIG. 4 is a sectional side view showing significant parts of an organicelectroluminescent device according to a second exemplary embodiment ofthe present invention. FIG. 4 shows the organic electroluminescentdevice 20. A significant difference between the organicelectroluminescent device 20 shown in FIG. 4 and the organicelectroluminescent device 1 shown in FIG. 1 is that, in the organicelectroluminescent device 20 shown in FIG. 4, an inorganic ion exchangelayer 22 is formed between a hole injection/transport layer 21 and alight-emitting layer 9.

In other words, in the organic electroluminescent device 20 shown inFIG. 4, the hole injection/transport layer 21 is formed with only theoriginal material to form the hole injection/transport layer, somewhatdifferent from the hole injection/transport layer 8 shown in FIG. 1.Accordingly, the hole injection/transport layer 21 formed of theoriginal material to form the hole injection/transport layer willcontain many Na ions as its ionic impurities as described above, andfrom this, these Na ions easily diffuse as mobile ions.

However, in the present exemplary embodiment, the inorganic ion exchangelayer 22 is formed between the hole injection/transport layer 21 and thelight-emitting layer 9. The inorganic ion exchange layer 22 is formed ofthe inorganic ion exchange material as mentioned above, and forinstance, is formed by mixing this inorganic ion exchange material withconductive resin, arranging the mixed inorganic ion exchange material onthe hole injection/transport layer 21 by a liquid droplet ejectionmethod, thereby forming a film. Depending on the types of the inorganicion exchange material, the vapor deposition method can be used to form afilm.

The light-emitting layer 9 is formed on the inorganic ion exchange layer22, and further a cathode 4 is formed on the light-emitting layer 9.Further, in the same manner as in the first exemplary embodiment, anelectron injection/transport layer (not shown) is formed on the bluelight-emitting layer. Moreover, a sealing layer 11 is formed on thecathode 4, thereby forming the organic electroluminescent device 20.

In the organic electroluminescent device 20 having the aboveconstruction, the inorganic ion exchange layer 22 is provided betweenthe hole injection/transport layer 21 and the light-emitting layer 9.Thus, when the Na ions that are ionic impurities existing, especially,in the hole injection/transport layer 21 become mobile ions and diffuse,they can be trapped and fixated by the inorganic ion exchange layer 22.Accordingly, the light-emitting property can be prevented fromdegrading, or such degradation can be reduced, due to the diffusion ofNa ions into light-emitting layer 9, for example, the lifespan can beprevented from shortening or such shortening can be reduced.

Further, for example, even when Sn ions in the transparent electrode 3diffuse, these ions will be trapped and fixated and be prevented fromdiffusing, or such diffusion can be reduced, into the light-emittinglayer 9 and degrading the light-emitting property.

Third Exemplary Embodiment

FIG. 5 is a sectional side view showing significant parts of an organicelectroluminescent device according to a third exemplary embodiment ofthe present invention. FIG. 5 shows the organic electroluminescentdevice 30. A significant difference between the organicelectroluminescent device 30 shown in FIG. 5 and the organicelectroluminescent device 20 shown in FIG. 4 is that, in the organicelectroluminescent device 30 shown in FIG. 5, an inorganic ion exchangelayer 32 is formed between a light-emitting layer 9 and an electroninjection/transport layer 31.

The inorganic ion exchange layer 32 is formed of the inorganic ionexchange material described in the first exemplary embodiment, similarto the inorganic ion exchange layer 22 shown in FIG. 4. In other words,for example, the inorganic ion exchange layer is formed by mixing thisinorganic ion exchange material with conductive resin, and arranging themixed inorganic ion exchange material on a hole injection/transportlayer 21 by a liquid droplet ejection method. Depending on types of theinorganic ion exchange material, the vapor deposition method can also beused to form a film.

An electron injection/transport layer 31 is provided when the bluelight-emitting layer is formed of, especially, a polymeric material, andis formed from the selective vapor deposition of LiF onto thelight-emitting layer (blue light-emitting layer) 9 with a mask. Theelectron injection/transport layer 31 formed of LiF is for efficientinjection/transport of electrons from the cathode 4 of Ca/Al formedthereon to the light-emitting layer 9.

Further, if the electron injection/transport layer 31 comes in directcontact with the light-emitting layer 9 in the same way as in therelated art or conventional manner, the Li ions in the electroninjection/transport layer 31 will become mobile ions and diffuse intothe light-emitting layer 9. Then, while these Li ions stay in thesurface of the light-emitting layer 9, i.e., the interface with theelectron injection/transport layer 31, they will function to attract theelectrons from the cathode 4 to the light-emitting layer 9, and thiswill improve the injection property/transportability of electrons.

However, as some time elapses, the Li ions will diffuse into the centerof the light-emitting layer 9, and the function to attract electronswill diminish, whereas the light-emitting efficiency of thelight-emitting layer 9 or the luminance thereof will degrade, eventuallyshortening the lifespan.

Therefore, in the present exemplary embodiment, the inorganic ionexchange layer 32 is formed between the light-emitting layer 9 and theelectron injection/transport layer 31 as described above. From thisformation of the inorganic ion exchange layer 32, the Li ions from theelectron injection/transport layer 31 will be trapped and fixated in theinorganic ion exchange layer 32, and this allows the light-emittingproperty to be prevented from degrading, or such degradation can bereduced, due to diffusion of the Li ions into the light-emitting layer9, for example or the lifespan to be prevented from shortening or suchshortening can be reduced. Also, even when the Ca ions in the cathode 4diffuse, they can be trapped and fixated and be prevented fromdiffusing, or such diffusion can be reduced, into the light-emittinglayer 9, thereby preventing or reducing degrading of the light-emittingproperty.

In the present exemplary embodiment, it is also preferred that theinorganic ion exchange layer 32 be formed by the liquid droplet ejectionmethod (ink jet method). By adopting the liquid droplet ejection method,the inorganic ion exchange material can be selectively or preciselydisposed only on the blue light-emitting layer. Accordingly,reliability, such as the lifespan characteristics in the bluelight-emitting layer, can be satisfactorily secured. Also, when adoptingthe liquid droplet ejection method, it can be conducted by mixing theinorganic ion exchange material with conductive resin, and dissolving itin a suitable solvent or dispersing in a suitable dispersion medium.

In the organic electroluminescent device 30 having the aboveconstruction, the inorganic ion exchange layer 32 is formed between thelight-emitting layer 9 and the electron injection/transport layer 31.Thus, the Li ions from the electron injection/transport layer 31 will betrapped and fixated in the inorganic ion exchange layer 32, which willprevent or reduce the Li ions from diffusing into the light-emittinglayer 9 and degrading the light-emitting property, and for instance,shortening the lifespan. Even when the Ca ions in the cathode 4 diffuse,they will be trapped and be prevented from diffusing, or such diffusioncan be reduced, into the light-emitting layer 9, and degrading thelight-emitting property can be reduced or prevented.

The present invention is not limited to the first, second and thirdexemplary embodiments, and various alterations can be made as long asthey do not depart from the scope of the present invention.

For example, the hole injection/transport layer 8 as the carrierinjection/transport layer was formed by adding an inorganic ion exchangematerial in the first exemplary embodiment, but when forming an electroninjection/transport layer with a polymeric material, the metallicion-trapping materials mentioned above may be added to the material toform the electron injection/transport layer.

When done this way, by trapping and fixating the metallic ions (ionicimpurities) from the cathode 4 or the metallic ions (ionic impurities)existing in the electron injection/transport layer by an inorganic ionexchange material to confine the ions in an electron injection/transportlayer, the diffusion of these metallic ions (ionic impurities) into thelight-emitting layer 9 which degrades the light-emitting property, suchas the lifespan, can be reduced or prevented.

Also, the inorganic ion exchange material may be directly added to thematerial to form the light-emitting layer and this may be used to formthe light-emitting layer. Then, even if the metallic ions diffuse fromthe hole injection/transport layer which is the carrierinjection/transport layer or the electron injection/transport layer, andfurther from the transparent electrode 3 or the cathode 4, they can betrapped and fixated by the inorganic ion exchange material, making itpossible to reduce or prevent the light-emitting property from degradingdue to the metallic ions.

Further, in the second and third exemplary embodiments, the inorganicion exchange layer 22 (32) was provided only either between the holeinjection/transport layer 21 and the light-emitting layer 9 or betweenthe light-emitting layer 9 and the electron injection/transport layer31. However, the inorganic ion exchange layer 22 and the inorganic ionexchange layer 32 may be provided on both sides.

Further, in the above exemplary embodiments, a polymeric material isused as the material to form the light-emitting layer 9, but a lowmolecular material may also be used to form the light-emitting layer 9.In that case, it is preferred that the electron injection/transportlayer is provided in all of the light-emitting layers, not just on theblue light-emitting layer, and that an inorganic ion exchange layer isprovided between every light-emitting layer and electroninjection/transport layer.

Moreover, the exemplary embodiments have described about applying thepresent invention to a bottom emission type organic electroluminescentdevice, but the present invention is not limited to this type, and canalso be applied to a so-called top emission type organicelectroluminescent device, where light is emitted from the opposite sideof the substrate.

The organic electroluminescent device of the present invention aspreviously described can be suitably used as a display for portableinformation processors, such as word processors and personal computers,or electronic apparatuses, such as portable phones and wristwatch-typeelectronics, for example.

1. An organic electroluminescent device, comprising: a first electrode;a second electrode; and a functional layer having at least alight-emitting layer and a hole injection/transport layer between thefirst electrode and the second electrode, the hole injection/transportlayer including a hole injection/transport material and an inorganic ionexchange material.
 2. The organic electroluminescent device according toclaim 1, the inorganic ion exchange material being antimony pentoxidehydrate.